An air spring, also known as an air bag or an air bellow, is a type of vehicle suspension powered by an electric or engine driven air pump or compressor. This pump pressurizes the air, using compressed air as a spring. Air suspension is often used in place of conventional steel springs, and in heavy vehicle applications such as buses and trucks. The purpose of air suspension is to provide a smooth, constant ride quality and in most cases it is self-leveling. Air pressure rises the spring and in turn raises the chassis from the axle.
One problem associated with known air springs is that the spring rate is not linear and exponentially grows as the spring compresses. Spring Rate is the amount of weight needed to compress a spring a certain distance. Springs are typically rated in LB/in (in metric system kg/mm), or specifically, how many pounds of weight are required to depress the spring by one inch. Consider you have 2 springs having different spring rates: one with 500 g/mm and the other with 750 g/mm. This means the 1st spring will compress 1 mm if you put a load of 500 grams, while the 2nd one will not. The 2nd one will need a 750 gram load to compress 1 mm. The common description of air springs is to say that the 2nd spring is harder than the 1st one, or that the springs that have a low spring rate are soft, while springs that have a high spring rate are stiff. If there are two different values listed for the spring rate of a spring, it means that the spring starts at one rate, and ends at another rate under full compression. This is associated with the air spring rate being non-linear and growing exponentially as the spring compresses.
A typical air spring has a relatively non-linear spring rate. See FIG. 1. This means that the force required to compress the air spring the first few inches of compression displacement is relatively the same, i.e. the spring rate remains pretty constant (between 500 lb/in and 1000 lb/in for the first 4 inches of compression displacement in FIG. 1). Then, the force required to compress the spring grows exponentially the remaining distance of compression displacement (grows from 1,000 lb/in to 12,000 lb/in for the compression displacement of 4 to 8 inches in FIG. 1). This non-linear spring rate provided by standard air springs is not desired as it varies the ride of the vehicle under different loads. This is especially problematic for vehicles required to carry heavier loads like commercial and military vehicles, where the vehicle is carrying no loads in some instances, small loads in other instances, and larger heavy loads in other instances.
A strut used in the suspension of a vehicle is commonly known as the MacPherson strut, which is a type of car suspension system which uses the axis of a telescopic damper as the upper steering pivot. It is widely used in modern vehicles and named after Earle S. MacPherson, who developed the design. MacPherson struts typically consist of a wishbone or a substantial compression link stabilized by a secondary link which provides a bottom mounting point for the hub or axle of the wheel, which provides both lateral and longitudinal forces on the wheel. The upper part of the hub is rigidly fixed to the inner part of the strut proper, the outer part of which extends upwards directly to a mounting in the body shell of the vehicle. The strut also usually has a steering arm built into the lower inner portion. The strut will usually carry both the coil spring on which the body is suspended and the shock absorber, which is usually in the form of a cartridge mounted within the strut. The whole assembly is very simple and can be preassembled into a unit, is relatively inexpensive and thus has been around and used frequently since its creation. However, there are no known air springs that can function as such Macpherson struts.
The instant invention is designed to address the above mentioned problems by providing an air spring, air strut and air suspension system with a more linear spring rate.